The present invention relates to a method as defined in the preamble of claim 1 for spraying a medium mist, especially a medium mist used in firefighting, in which method at least two sprays of medium mist are formed, of which a first spray is within a second medium mist spray at least at or near the spraying point.
The invention also relates to a spraying nozzle as defined in claim 6, comprising a frame with an inlet formed in it, a first nozzle chamber with a first nozzle opening, a second nozzle chamber with a discharge opening formed as a ring-like opening around the discharge opening of the first nozzle chamber, and at least one medium passage from the inlet to each nozzle chamber.
On the other hand, various spraying nozzles for producing a liquid mist are known. In prior art, nozzles using a so-called swirl chamber inside the nozzle are known. Even with a low pressure, such nozzles can easily produce a good uniform spray, which “swirls” because the water is passed tangentially into the swirl chamber and the mist spray is discharged out of the nozzle in an orbicular fashion. In this case, too, the cross-sectional, pattern of the spray produced as seen perpendicularly to the main spraying direction is circular, in other words, the middle area within the spray is not covered but remains void of mist. It has been possible to correct this deficiency by using a nozzle that forms a full spraying cone. In addition to the foregoing, nozzles of this type produce a spray that conies out straight from the center of the nozzle. This should make the spray a full cone. This may work if the swirling circle is not very large and the pressure is fairly high. Experience shows, however, that the middle spray forms large drops, and therefore the mist produced by the nozzle is not of uniform quality. A nozzle applying such a solution is disclosed in U.S. Pat. No. 6,129,154. This solution, too, involves the problem that the mist can not be spread over a sufficiently large area, especially when relatively low pressures are used.
Especially fire extinguishing systems using water mist require a spray that covers a sufficiently large area. The sprinkler nozzles used in traditional fire extinguishing systems are provided with a barrier plate placed in front of the spray discharged from the nozzle head to spread the spray over a large area. Such sprays are not mist-like and these nozzle heads involve the problem that they leave a void in the middle area of the spray, where no extinguishing medium can be sprayed by the nozzle head.
The object of the present invention is to create a completely new type of solution that makes it possible to produce a homogeneous spray that is spread over a large area. Thus, the aim is to spread the mist over a sufficiently large area and so that a good mist coverage is achieved and, on the other hand, so that the flow of the sprayed medium is about the same in the whole coverage area. It is thus also an aim to ensure that no so-called voids are left in the spraying pattern produced. Yet another objective of the invention is to create a nozzle especially for use in connection with relatively low pressures. Yet another objective of the invention is to achieve a solution for a nozzle for use in firefighting that is especially suited for the spraying of water mist.